1. Field of the Invention
The present invention relates to a plastic display process, and more particularly, to a method of transferring a thin film device, such as a thin film transistor (TFT), onto a plastic sheet adapted for use in a plastic display process.
2. Description of the Related Art
Liquid crystal displays (LCDs) have been widely adopted as information displays in, for example, calculators, watches, video games, audio and video equipment, portable computers, car dashboards, and the like. LCDs are also widely used in mobile devices especially where low weight is a desired feature.
The substrates used in such devices are typically glass plates having a thickness in the range from 0.7 to 1.1 mm. Due to the high specific weight of glass, the total weight of a display is mainly determined by the size and thickness of the glass plate used. Additionally, glass plates are hard to bend, and hinder LCDs from achieving flexibility. Therefore, it is important to investigate a light and flexible material for use in substrates.
In some applications, plastic sheets are used as low-weight substrates in LCDs. The high strength and flexibility of plastics enable the manufacture of flexible displays. However, during the high temperature thermal process of manufacturing an active device, such as forming a thin film transistor (TFT) directly on a plastic sheet, the plastic sheet will be subjected to stress and strain. That is, because the difference of the expansion coefficient between the plastic sheet and the thin film of a TFT is very great, the thin film can separate or crack during repeated thermal cycle processes, seriously affecting device reliability and yield.
In U.S. Pat. No. 6,372,608 and in the article entitled xe2x80x9cLow Temperature Poly-Si TFT LCD Transferred onto Plastic Substrate Using Surface Free Technology by Laser Ablation/Annealingxe2x80x9d in the Journal of Asia Display/IDW 2001, pp. 339-342, Shimoda et al disclose an exfoliating method for dividing a thin film device from a glass substrate by high energy laser beam. Though effective, this method nevertheless requires expensive laser equipment.
In the article entitled xe2x80x9cLow Temperature Polycrystalline-Silicon TFT Color LCD Panel Made of Plastic Substratesxe2x80x9d in the Journal of SID DIGEST 2002, pp. 1196-1199, Asano et al disclose an exfoliating method for dividing a thin film device from a glass substrate by HF etching. This method, however, presents the problems of thin film device damage caused by strong acid and a dangerous working environment.
The object of the present invention is to provide a method of forming a flexible LCD.
Another object of the present invention is to provide a method of transferring a thin film device, such as a thin film transistor (TFT), onto a plastic sheet adapted for use in a flexible display process, without damage due to excessive heat in the TFT process.
In order to achieve these objects, the present invention provides a method of transferring a thin film device onto a plastic sheet. A silver-containing buffer layer is formed on a glass substrate. A transferred layer including a thin film device is formed on part of the silver-containing buffer layer, wherein at least one first hole penetrates the transferred layer to expose the silver-containing buffer layer and an edge of the silver-containing buffer layer is also exposed. A first plastic layer including at least one second hole is adhered to the transferred layer with a removable glue, wherein the second hole corresponds to the first hole, and part of the first plastic layer is located above the edge of the silver-containing buffer layer. The silver-containing buffer layer is oxidized to expand, thereby separating the silver-containing buffer layer from the transferred layer. A second plastic layer is adhered to the transferred layer. The removable glue is eliminated to remove the first plastic layer.
The present invention improves on the prior art in that the present method utilizes the expansive property of silver to transfer the thin film device from the glass plate onto a plastic sheet without damage due to excessive heat in the TFT process. Thus, the invention is suitable for the fabrication of flexible plastic displays. In addition, the present method does not require expensive laser equipment and strong acid to remove the glass plate, thereby reducing costs, improving workplace safety and ameliorating the disadvantages of the prior art.